Is the Buufalo just a modem? I gather it is or it doesn't make sense. Have you got something against getting a modem/router - combined modem and router all in one case, no additional wiring?
You can get internet connection, using the Network function in Control Panel with Windows, to connect your pc to a router - by wifi (if you have a wifi card) or by ethernet cable if you have an ethernet port on your pc.
The router has antennae and ethernet ports for you to connect to.
So, in your case, the internet is transferred from the modem to the router to your pc.
Your internet plan determines the maximum speed everything can run at. The modem then will determine what speed it can send to the router and the router will determine what speed and signal strength that it can send to your pc - by cable or wifi. Your wifi card will determine how fast the signal is going from it to your computer.
So - I was hoping you would provide me with 'links' - internet addresses - of the websites that have the info/specs on - your modem, your router and your wifi card. This will tell me how fast everything CAN go.
If you've replaced on of your current bits and want to be able to compare it to an old bit that you used to use, then I'd also need the link to that device too. Otherwise we're just shooting the breeze and using generalisations.